A method of vacuum-assisted RTM is known which disposes a resin distribution medium over the whole of one surface of a reinforcing-fiber substrate (usually, a reinforcing-fiber substrate formed as a preform), covers the whole with a bag material to reduce the pressure inside the bag material, injects a resin toward the resin distribution medium, first, distributes the injected resin substantially in in-plane directions of the resin distribution medium and, thereafter, impregnates the resin into the reinforcing-fiber substrate in its thickness direction. In such a method of vacuum-assisted RTM, in a case where the resin flowability of the preform is nonuniform, because there occurs a difference between times for flow of the resin in the preform being impregnated into the preform, a problem may occur that a non-impregnated part is generated, or that a previously impregnated resin interrupts a suction route between a pressure-reduced suction port and the preform, and a following resin impregnation is impaired. For example, in a case where parts different in thickness exist in the preform, or in a case where parts different in length or width to be impregnated with resin (parts different in resin impregnation length) exist in the lengthwise direction of the preform, because there occurs a difference between times for flow of the resin in the preform depending upon these parts, a problem may occur that a non-impregnated part is generated, or that a previously impregnated resin impairs a following resin impregnation.
To increase the resin distribution property due to the resin distribution medium and improve the surface property of a molded product in the method of vacuum-assisted RTM, although a technology is known for increasing the number of disposed resin distribution media (for example, JP-A-2004-188750), by merely increasing the number of resin distribution media over the entire surface, although the inner flowability of the resin distribution medium itself can be improved, the above-described problems cannot be solved in a case where there is a change in resin flowability of reinforcing-fiber substrate when the resin is impregnated from the resin distribution medium into the reinforcing-fiber substrate. Further, because a large amount of resin is distributed at the part of resin distribution medium, waste of resin may become great.
Further, although a method is also proposed for providing many resin injection ports when a large-sized plane material is molded by vacuum-assisted RTM (for example, JP-A-2003-011136), even if the resin impregnation into a resin distribution medium is improved, the aforementioned problems cannot be solved in a case where there is a change in resin flowability of reinforcing-fiber substrate when the resin is impregnated from the resin distribution medium into the reinforcing-fiber substrate.
Furthermore, although a technology is also proposed for using a net-like stereo structured resin distribution medium (for example, JP-A-2004-249527), it does not describe as to a solution for the problem due to a change in resin flowability of reinforcing-fiber substrate.
Accordingly, it could be helpful to provide a method of vacuum-assisted RTM, in a case where there is a change in resin flowability in in-plane directions of a reinforcing-fiber substrate, which can absorb the change by the side of a resin distribution medium, and with respect to a resin-impregnated reinforcing-fiber substrate becoming a product or a main structural part of a product, which can prevent a problem that a non-impregnated part is generated or a problem that a previously impregnated resin impairs a following resin impregnation from occurring, and can stably obtain a desired molded product surely.